CRETACEOUS PTERODACTYLES. 445 



(figs. 7 and 8, c, d) is sub-triangular, convex transversely, concave in the opposite 

 direction, with the lower angle continued down upon the side of the thickest part 

 of this anterior portion of the sternum. The back part of the articular surface 

 rises higher than the front, so that the general aspect of the surface is obliquely 

 upward, forward, and outward. The two surfaces are separated by a non-articular 

 depression y), of the breadth of one coracoid surface; this depression is bounded, 

 like the sella turcica of the human sphenoid, by a transverse rising or ridge of 

 bone (fig. 7, a), continued between ihe hinder angles of the two articular surfaces, 

 and in front by the manubrial tubercle (4), from which the upper border of the 

 produced keel is continued. The sternum contracts behind the articular region at 

 g, figs. 8 and 9, and then expands rapidly in the horizontal direction, to form the 

 broad, lamelliform body of the bone {h), which, in Pterodactylus sueviciis,* appears 

 to have been almost semicircular in shape, and to have extended backward 

 beneath about one half of the thoracic abdominal cavity. The upper surface of 

 the fore part of the sternal plate is concave, and it becomes flatter as it expands. 

 The lateral and lower surfaces are also concave vertically, with linear markings, 

 showing the implantation of the pectoral muscles that filled those concavities on 

 each side the keel. Sufficient thickness of the bone remains at the fractured 

 posterior part (/•), where the keel has not subsided, to show the widely cancellous, 

 and seemingly pneumatic, texture of the bone. 



The similar, but smaller and more mutilated, portion of a sternum of a Ptero- 

 dactyle (PI. 12, figs. 10 — 12) shows the same form and position of the coracoid 

 articular surfaces, the non-articular intermediate depression, the lateral emargi- 

 nations or contraction of the sternum behind the part supporting the coracoids, 

 and the backward extension of the keel beneath a certain proportion of the 

 expanded body of the sternum, forming the hollows for the lodgment of the 

 pectoral muscles. 



A sternum of the shape and proportions above described plainly indicates 

 pectoral muscles of great bulk and strength, by the extent of origin it afforded to 

 them, and by the depth of the depressions they filled on each side of the keel ; but 

 to what purpose the limbs moved by those muscles were put is best inferred from 

 the characters of the bone into which they were inserted. If, however, the peculiar 

 development of the fore limbs of the Pterodactyle had not been known, the 

 evidence of a pneumatic or widely cancellous structure in the thicker fore part of 

 the breast-bone would have suggested a power of locomotion in its original possessor 

 akin to that of the class to the sternum of which that of the Pterodactyle makes, 

 upon the whole, the nearest approach. 



It is true that the sternum is broad and shield-shaped in the Apteryx and 

 other land-birds devoid of the power of flight; but this form, together with the 



* Quenstedt, op. cit. 



